1. Field of the Invention
This invention relates to a developer replenishment unit for replenishing a developing unit in an image formation apparatus such as an electrophotographic copier or printer with a developer and an image formation apparatus comprising the developer replenishment unit and in particular to a developer replenishment unit for notifying the user of the need for replenishing with toner and controlling prohibiting image formation depending on the remaining amount of toner and an image formation apparatus comprising the developer replenishment unit.
The invention can be used particularly suitably for a developer replenishment unit having a supply vessel (reserve tank) for temporarily storing toner in apart of a supply passage and an image formation apparatus comprising the developer replenishment unit.
2. Background Art
Since an electrophotographic copier, printer, etc., for the user frequently using the copier, printer, etc., consumes a large amount of toner, if a toner cartridge can contain a large amount of toner as much as possible, the number of cartridge replacing times can be lessened and the load on the user can be lightened. However, if one toner cartridge contains a large amount of toner, it is necessary to increase output of a motor for driving a toner transport member in the cartridge and there is a possibility that toner in the cartridge will coagulate. Since the cartridge also becomes large and heavy, the operability when the user replaces the cartridge, etc., worsens. Since a full-color machine needs to use four color toners, limitation on space is large and if only a black toner cartridge frequently used is put into a large capacity, there is a problem of increasing cost, etc.
To solve the problems, the following related arts are known:
Related Art (J01)
In Related art (J01), there provided a plurality of toner cartridges attached to and detached from an image formation apparatus (image formation means) and toner transport tubes being connected to the toner cartridges and merged at midpoint for transporting toner to a developing unit. A sensor for detecting the presence or absence of toner is placed after the toner transport tubes are merged.
In this art, cartridges of all colors can be made common and it is made possible to use a plurality of toner cartridges of only the color frequently used.
Related Art (J02)
In related art (J02), toner supplied from a toner cartridge is once stored in a toner reserve tank and then a developing unit is replenished with the toner.
Problem of Related Art (J01)
In the related art (J01), when toners in all toner cartridges run out or when only one of cartridges is placed and becomes empty of toner, toner scarcely remains in the toner transport tube and thus there is a problem of need for immediately prohibiting the image formation operation.
Problem of Related Art (J02)
In the related art (J02), the image formation operation can be performed in toner in the toner reserve tank for a while until the toner cartridge is replaced with a new one after the toner cartridge becomes empty of toner. However, there is a problem of increasing cost if a reserve tank and a remaining amount sensor for detecting the remaining amount of toner are provided for each toner cartridge.
It is therefore an object of the invention to provide a developer replenishment unit for replenishing a developing unit with toner and an image formation apparatus comprising the developer replenishment unit for making it possible to:
(O01) detect the presence or absence of toner in all toner cartridges without providing a reserve tank and without providing a remaining amount sensor for each toner cartridge;
(O02) continue image formation without prohibiting the image formation operation immediately when the placed toner cartridge becomes empty of toner; and
(O03) reduce the burden on the user at the cartridge replacing time and also decrease the cost without putting a cartridge containing toner frequently used and consumed in a large amount into a large capacity. Next, the invention solving the problems will be discussed. In the description of the invention, the reference numerals in parentheses following the components of the invention are those of the components of an embodiment described later corresponding to the components of the invention. The reason why the invention will be discussed with the components related to the reference numerals of the components of the embodiment described later is that understanding of the invention is facilitated; the scope of the invention is not limited to the embodiment.
To the ends, according to the invention, there is provided a developer replenishment unit comprising the following components (A01) to (A08):
(A01) two contiguous cartridge placement members (4k and 6k) each in which a developer cartridge (Kk) having a developer replenishment vessel (42k) for storing a replenishment developer therein, the developer replenishment vessel having a replenishment port (44k) for ejecting the stored developer, and a cartridge transport member (51+52) being supported for rotation in the developer replenishment vessel (42k) for ejecting the developer from the replenishment port (44k) when the cartridge transport member rotates is placed detachably;
(A02) a reserve tank (H2k) having an inflow port (4bk, 6bk) into which the developers ejected from the replenishment ports (44k) of the two developer cartridges (Kk) placed in the two contiguous cartridge placement members (4k and 6k), the two developer cartridges being named first and second developer cartridges (Kk1 and Kk2), flow, a circulation passage (11+12) for circulating the influent developer, and a supply port (16k) for ejecting the developer circulating in the circulation passage (11+12);
(A03) a supply transport member (23k) being supported for rotation in the reserve tank (H2k) for ejecting the developer in the reserve tank (H2k) from the supply port (16k) when the supply transport member rotates;
(A04) a developer transport member (1k) for transporting the developer ejected from the supply port (16k) to a developing unit (Gk) for developing an electrostatic latent image formed on an image support (PRk) surface to a toner image;
(A05) a cartridge drive (MB2k) having a first cartridge drive (MB2k1) and a second cartridge drive (MB2k2) for separately rotating the cartridge transport members (51+52) of the first cartridge (Kk1) and the second cartridge (Kk2);
(A06) a supply drive (MB1k) for rotating the supply transport member (23k) in the reserve tank (H2k);
(A07) a storage amount sensor (SN1k) for sensing whether or not the storage amount of the developer in the reserve tank (H2k) is a predetermined amount or more; and
(A08) cartridge control means (C5) for controlling operation of the cartridge drive (MB2k) so that the detection value of the storage amount sensor (SN1k) indicates presence.
In the developer replenishment unit of the invention, the number of the developer cartridges (Kk) is not limited to two and may be three or more (namely, at least two) That is, it is also possible to place three or more developer cartridges (Kk) in the three or more contiguous cartridge placement members (4k, 6k).
In the developer replenishment unit of the invention comprising the components (A01) to (A08), the cartridge transport member (51+52) of the developer cartridge (Kk) ejects the replenishment developer stored in the developer replenishment vessel (42k) from the replenishment port (44k) when the cartridge transport member rotates. The cartridge transport member (51+52) of the first cartridge (Kk1) and the second cartridge (Kk2) placed in the two contiguous cartridge placement members (4k and 6k) are rotated separately by the cartridge drive (MB2k) having the first cartridge drive (MB2k1) and the second cartridge drive (MB2k2). The developer ejected from each replenishment port (44k) of the first cartridge (Kk1) and the second cartridge (Kk2) flows through the inflow port (4bk, 6bk) into the reserve tank (H2k).
The developer flowing into the reserve tank (H2k) circulates in the circulation passage (11+12) in the reserve tank (H2k). The developer circulating in the circulation passage (11+12) is ejected from the supply port (16k) by the supply transport member (23k) supported for rotation in the reserve tank (H2k). The developer ejected from the supply port (16k) is transported by the developer transport member (1k) to the developing unit (Gk) for developing the electrostatic latent image formed on the image support (PRk) surface to a toner image. The one storage amount sensor (SN1k) placed in the reserve tank (H2k) senses whether or not the storage amount of the developer in the reserve tank (H2k) is a predetermined amount or more. The cartridge control means (C5) controls operation of the cartridge drive (MB2k) for making the developer flow into the reserve tank (H2k) so that the detection value of the storage amount sensor (SN1k) indicates presence.
Therefore, in the developer replenishment unit of the invention, one storage amount sensor (SN1k) detects the amount of the developer in the reserve tank (H2k) into which developers flow from the two developer cartridges (Kk), so that it is not necessary to place a sensor for each developer cartridge. That is, if two (a plurality of) developer cartridges (Kk) of frequently used color are used, the number of sensors for detecting the presence or absence of developer can be decreased and therefore the cost can be reduced.
Two (a plurality of) developer cartridges (Kk) containing color toner frequently used and consumed in a large amount are placed and when both the developer cartridges (Kk) become empty of developer, they are replaced at a time, whereby the number of developer cartridge (Kk) replacement times can be decreased and the burden on the user can be reduced. Further, since two (a plurality of) developer cartridges (Kk) are placed, it becomes unnecessary to put the developer cartridge (Kk) into a large capacity. Therefore, the need for handling a large and heavy developer cartridge (Kk) put into a large capacity is eliminated and the burden on the user at the cartridge replacing time can be reduced. Since the developer cartridge (Kk) is not put into a large capacity, the load on the motor can be decreased and a high-output motor need not be used, so that an increase in cost can be prevented. Further, since it is not necessary to put the developer cartridge (Kk) into a large capacity, all developer cartridges (Ky, Km, Kc, and Kk) can be formed as similar shapes and the components can be made common; the cost can be reduced.
The developer replenishment unit of the invention comprises the reserve tank (H2k) and thus if the developer in the placed developer cartridge (Kk) runs out, it is not necessary to immediately prohibit the image formation operation and the image formation operation can be continued using the developer stored in the reserve tank (H2k) for a while.
The developer replenishment unit of the invention comprising the components can also comprise the following components (A09) and (A010):
(A09) an empty state notification unit (UI1) for notifying the user that when either the first cartridge (Kk1) or the second cartridge (Kk2) is used, the cartridge being used becomes empty; and
(A10) empty state notification unit control means (C8) for operating the empty state notification unit (UI1) if it is made impossible for the detection value of the storage amount sensor (SN1k) to indicate presence when either the first cartridge (Kk1) or the second cartridge (Kk2) is used.
In the developer replenishment unit comprising the components (A09) and (A010), the empty state notification unit control means (C8) operates the empty state notification unit (UI1) if it is made impossible for the detection value of the storage amount sensor (SN1k) to indicate presence when either the first cartridge (Kk1) or the second cartridge (Kk2) is used. The empty state notification unit (UI1) notifies the user that when either the first cartridge (Kk1) or the second cartridge (Kk2) is used, the cartridge being used becomes empty.
Therefore, in the developer replenishment unit of the invention, if the developer cartridge (Kk) cannot immediately be replaced because there is no spare on hand, etc., the image formation operation is not prohibited and can be continued using the developer in the other developer cartridge (Kk) or the developer in the reserve tank (H2k).
The developer replenishment unit of the invention comprising the components can also comprise the following components (A011) and (A012):
(A011) consumption amount detection means (C3) for detecting the consumption amount of the developer of the developing unit (Gk); and
(A012) supply control means (C4) for controlling operation of the supply drive (MB1k) so as to eject the developer from the supply port (16k) in response to the consumption amount detected by the consumption amount detection means (C3).
In the developer replenishment unit of the invention comprising the components, the consumption amount detection means (C3) detects the consumption amount of the developer consumed in the developing unit (Gk). The supply control means (C4) controls operation of the supply drive (MB1k) so as to eject the developer from the supply port (16k) in response to the consumption amount detected by the consumption amount detection means (C3). Therefore, the developer is supplied from the reserve tank (H2k) in response to the amount of the developer consumed in the image formation operation. The reserve tank (H2k) is replenished with the developer from the developer cartridge (Kk) in response to the detection result of the storage amount sensor (SN1k) of the reserve tank (H2k). Consequently, the storage amount of the developer in the reserve tank (H2k) is held almost constant, and the developer supply rate (dispense rate) from the reserve tank (H2k) to the developing unit (Gk) is also held almost constant.
The developer replenishment unit of the invention comprising the components can also comprise the following components (A013) to (A017):
(A013) the inflow port (4bk, 6bk) having a first inflow port (4bk) and a second inflow port (6bk) into which the developers ejected from the replenishment ports (44k) of the first cartridge (Kk1) and the second cartridge (Kk2) flow separately;
(A014) the second inflow port (6bk) and the first inflow port (4bk) being placed in order as they are from the storage amount sensor (SN1k) to the upstream side of the circulation passage (11+12) in the reserve tank (H2k);
(A015) the first cartridge drive (MB2k1) for operating the cartridge transport member (51+52) of the first cartridge (Kk1) only for a setup replenishment time (tb) for replenishing the reserve tank (H2k) with the developer in the first cartridge (Kk1) each time the supply time of the operation time of the supply drive (MB1k) reaches a setup value (ta, tc) while the first cartridge (Kk1) is used;
(A016) supply time setup value storage means (C6) for storing the setup value (ta, tc) of the supply time while the first cartridge (Kk1) is used; and
(A017) replenishment time setup value storage means (C7) for storing the setup value (tb) of the replenishment time while the first cartridge (Kk1) is used.
In the developer replenishment unit of the invention comprising the components (A013) to (A017), the developer ejected from the first cartridge (Kk1) flows into the first inflow port (4bk) and the developer ejected from the second cartridge (Kk2) flows into the second inflow port (6bk) separate from the first cartridge (Kk1) The second inflow port (6bk) and the first inflow port (4bk) are placed in order as they are from the storage amount sensor (SN1k) to the upstream side of the circulation passage (11+12) in the reserve tank (H2k). The first cartridge drive (MB2k1) operates the cartridge transport member (51+52) of the first cartridge (Kk1) only for the setup replenishment time (tb) for replenishing the reserve tank (H2k) with the developer in the first cartridge (Kk1) each time the supply time of the operation time of the supply drive (MB1k) reaches the setup value (ta, tc) while the first cartridge (Kk1) is used.
Therefore, in the first cartridge (Kk1) for allowing the developer to flow in from the first inflow port (4bk) upstream apart from the storage amount sensor (SN1k), the cartridge transport member (51+52) operates every setup supply time (ta, tc) and the developer is ejected. Since it takes time until the developer flowing in from the first inflow port (4bk) is transported to the location where the storage amount sensor (SN1k) is placed, if the developer is replenished, the detection value of the storage amount sensor (SN1k) does not indicate presence and the developer may be over replenished or when the detection value of the storage amount sensor (SN1k) indicates presence, the storage amount of the developer in the reserve tank (H2k) may over lessen.
However, in the developer replenishment unit of the invention, for example, the setup value (ta, tc) of the supply time is not only set so as to operate the cartridge transport member (51+52) if the storage amount sensor (SN1k) detects developer absence, but also set so as to operate the cartridge transport member (51+52) while the storage amount sensor (SN1k) detects developer presence, whereby the storage amount in the reserve tank (H2k) can be adjusted. Therefore, in the developer replenishment unit of the invention, if developers flow in from the two separate inflow ports of the first inflow port (4bk) and the second inflow port (6bk), the storage amount of the developer in the reserve tank (H2k) can be maintained in a predetermined range using the one storage amount sensor (SN1k) and the dispense rate can be held a predetermined value.
To the ends, according to the invention, there is provided an image formation apparatus comprising a developer replenishment unit (Hk) comprising the components described above.
Since the image formation apparatus of the invention comprising the components comprises the developer replenishment unit (Hk) comprising the components, the developer storage amount in the reserve tank (H2k) into which developers flow from the two developer cartridges (Kk) can be adjusted based on the detection value of the one storage amount sensor (SN1k). If two (a plurality of) developer cartridges of frequently used color (Kk) are used, it becomes unnecessary to provide the storage amount sensor (SN1k) for detecting the presence or absence of developer for each developer cartridge and therefore the cost can be reduced.
Two (a plurality of) developer cartridges (Kk) containing color toner frequently used and consumed in a large amount are placed and when all the developer cartridges (Kk) become empty of developer, they are replaced at a time, whereby the number of developer cartridge (Kk) replacement times can be decreased and the burden on the user can be reduced. Since it becomes unnecessary to put the developer cartridge (Kk) into a large capacity, the burden on the user at the cartridge replacing time as the cartridge becomes heavy and large can be lightened. Since the developer cartridge (Kk) is not put into a large capacity, the load on the motor can be decreased and a high-output motor need not be used, so that an increase in cost can be prevented. Further, all color developer cartridges (Ky, Km, Kc, and Kk) are formed as similar shapes, whereby the parts can be made common, and the cost can be reduced.
The developer replenishment unit of the invention comprises the reserve tank (H2k) and thus if the developer in the used developer cartridge (Kk) runs out, the image formation operation is not immediately prohibited and can be continued using the developer in the reserve tank (H2k) for a while.
To the ends, according to the invention, there is provided an image formation apparatus comprising the following components (B01) to (B09):
(B01) Y (yellow), M (magenta), C (cyan), and K (black) color toner image formation units (Uy, Um, Uc, and Uk) each comprising a rotating image support (PRy, PRm, PRc, PRk) with a surface passing through a charging area, a latent image formation position (Q1y, Q1m, Q1c, Q1k), a developing area (Q2y, Q2m, Q2c, Q2k), a primary transfer area (Q3y, Q3m, Q3c, Q3k), and a cleaning area in order, a charger (CRy, CRm, CRc, CRk) for uniformly charging the image support (PRy, PRm, PRc, PRk) surface in the charging area, a latent image formation unit (ROS) for forming an electrostatic latent image on the charged image support (PRy, PRm, PRc, PRk) surface at the latent image formation position (Q1y, Q1m, Q1c, Q1k), a developing unit (Gy, Gm, Gc, Gk) for developing the electrostatic latent image to a toner image in the developing area (Q2y, Q2m, Q2c, Q2k), and a cleaner (CLy, CLm, CLc, CLk) for collecting in the cleaning area the remaining toner on the image support (PRy, PRm, PRc, PRk) surface with the toner image primary-transferred to an intermediate transfer belt (B) when the image support surface passes through the primary transfer area (Q3y, Q3m, Q3c, Q3k);
(B02) the Y (yellow), M (magenta), C (cyan), and K (black) color developing units (Gy, Gm, Gc, Gk) each having a developer vessel for storing a developer containing Y (yellow), M (magenta), C (cyan), K (black) color toner and a developing roll being supported on the developer vessel for rotation for transporting the developer deposited on a surface of the developing roll to the developing area (Q2y, Q2m, Q2c, Q2k) opposed to the image support (PRy, PRm, PRc, PRk) and developing the electrostatic latent image formed on the image support surface to a toner image;
(B03) a belt module (BM) having the intermediate transfer belt (B) for passing through the primary transfer areas (Q3y, Q3m, Q3c, Q3k) in order for coming in contact with the image support (PRy, PRm, PRc, PRk) surfaces of the Y (yellow), M (magenta), C (cyan), and K (black) color toner image formation units (Uy, Um, Uc, and Uk) in order to which the toner images on the image support (PRy, PRm, PRc, PRk) surfaces are transferred in order in an overlap manner, a plurality of belt support rolls (Rt, Rw, Rf, and T2a) including a belt drive roll (T2a) and a plurality of driven rolls (Rt, Rw, and Rf) for supporting the intermediate transfer belt (B), a primary transfer device (T1y, T1m, T1c, T1k) for transferring the toner images on the image support (PRy, PRm, PRc, PRk) surfaces to the belt (B) surface in the primary transfer area (Q3y, Q3m, Q3c, Q3k), and a belt frame for supporting the intermediate transfer belt (B), the belt support rolls (Rt, Rw, Rf, and T2a), and the primary transfer device (T1y, T1m, T1c, T1k);
(B04) a secondary transfer device (T2) for secondary-transferring the toner images primary-transferred in order onto the intermediate transfer belt (B) onto a record sheet (S);
(B05) a fuser (F) for fixing the toner images secondary-transferred onto the record sheet (S);
(B06) Y (yellow), M (magenta), C (cyan), and K (black) color cartridge placement members (4k, 6y, 6m, 6c, and 6k) in which Y (yellow), M (magenta), C (cyan), and K (black) color developer cartridges (Ky, Km, Kc, and Kk) having developer replenishment vessels (42y, 42m, 42c, and 42k) for storing replenishment Y (yellow), M (magenta), C (cyan), and K (black) color developers therein, each of the developer replenishment vessels having a replenishment port (44y, 44m, 44c, 44k) for ejecting the stored developer, and cartridge transport members (51+52) being supported for rotation in the developer replenishment vessels (42y, 42m, 42c, and 42k) for ejecting the developers from the replenishment ports (44y, 44m, 44c, and 44k) when the cartridge transport members rotate are placed detachably;
(B07) a reserve tank (H2k) for K (black) color, having an inflow port (4bk, 6bk) into which the developers ejected from the replenishment ports (44k and 44k) of the K (black) color cartridges placed contiguous to each other, the K (black) color cartridges being named first and second cartridges (Kk1 and Kk2), flow, a circulation passage (11+12) for circulating the influent developer, and a supply port (16k) for ejecting the developer circulating in the circulation passage (11+12);
(B08) a supply transport member (23k) being supported for rotation in the reserve tank (H2k) for ejecting the developer in the reserve tank (H2k) from the supply port (16k) when the supply transport member rotates; and
(B09) a K (black) color developer transport member (1k) for transporting the K (black) color developer ejected from the supply port (16k) to a developing vessel of the K (black) color developing unit (Gk).
The image formation apparatus of the invention comprising the components (B01) to (B09) is a full-color tandem image formation apparatus. The Y (yellow), M (magenta), C (cyan), and K (black) color toner image formation units (Uy, Um, Uc, and Uk) comprise the rotating image supports (PRy, PRm, PRc, and PRk), the chargers (CRy, CRm, CRc, and CRk), the latent image formation units (ROS), the developing units (Gy, Gm, Gc, and Gk), and the cleaners (CLy, CLm, CLc, and CLk). The Y (yellow), M (magenta), C (cyan), and K (black) color developer cartridges (Ky, Km, Kc, and Kk) are placed detachably in the Y (yellow), M (magenta), C (cyan), and K (black) color cartridge placement members (4k, 6y, 6m, 6c, and 6k). In the Y (yellow), M (magenta), C (cyan), and K (black) color developer cartridges (Ky, Km, Kc, and Kk), when the cartridge transport members (51+52) in the developer replenishment vessels (42y, 42m, 42c, and 42k) rotate, the developers stored in the developer replenishment vessels (42y, 42m, 42c, and 42k) are ejected from the replenishment ports (44y, 44m, 44c, and 44k). The developers ejected from the replenishment ports (44k and 44k) of the first and second cartridges (Kk1 and Kk2) flow into the reserve tank (H2k) for K (black) color through the inflow ports (4bk and 6bk). The influent developer circulates in the circulation passage (11+12). The supply transport member (23k) ejects the developer circulating in the reserve tank (H2k) from the supply port (16k). The K (black) color developer transport member (1k) transports the K (black) color developer ejected from the supply port (16k) to the developing vessel of the K (black) color developing unit (Gk). To replenish each developing units (Gc, Gm, Gk) with developer from the Y (yellow), M (magenta), C (cyan) developer cartridges (Ky, Km, Kc) other than K (black), it is also possible to supply the developer through the reserve tanks (H2y, H2m, H2c) as with K (black) or it is also possible to supply the developer directly by a transport member, etc., without providing the reserve tanks (H2y, H2m, H2c).
Therefore, two (a plurality of) developer cartridges (Kk) of K (black) frequently used are placed in the image formation apparatus of the invention, so that the K developer amount is large, the number of developer cartridge (Kk) replacement times can be decreased, and the burden on the user can be lightened. Since two (a plurality of) developer cartridges (Kk) are placed, it becomes unnecessary to put the developer cartridge (Kk) into a large capacity. Therefore, the need for handling a large and heavy developer cartridge (Kk) put into a large capacity is eliminated and the burden on the user at the cartridge replacing time can be reduced. Further, since it is not necessary to put the developer cartridge (Kk) into a large capacity, all developer cartridges (Ky, Km, Kc, and Kk) can be formed as similar shapes and the components can be made common; the cost can be reduced.
The reserve tank (H2k) is provided and thus if the developer in the placed developer cartridge (Kk) runs out, the image formation operation is not immediately prohibited and can be continued using the developer in the reserve tank (H2k) for a while.
The image formation apparatus of the invention comprising the components can further comprise the following components (B010) to (B013):
(B010) a K (black) color cartridge drive (MB2k) having a first cartridge drive (MB2k1) and a second cartridge drive (MB2k2) for separately rotating the cartridge transport members (51+52) of the first cartridge (Kk1) and the second cartridge (Kk2);
(B011) a supply drive (MB1k) for rotating the supply transport member (23k) in the K (black) color reserve tank (H2k);
(B012) a storage amount sensor (SN1k) for sensing whether or not the storage amount of the developer in the K (black) color reserve tank (H2k) is a predetermined amount or more; and
(B013) cartridge control means (C5) for controlling operation of the K (black) color cartridge drive (MB2k) so that the detection value of the storage amount sensor (SN1k) indicates presence.
In the image formation apparatus of the invention comprising the components (B010) to (B013), the cartridge transport members (51+52) of the first cartridge (Kk1) and the second cartridge (Kk2) are separately rotated by the K (black) color cartridge drive (MB2k) and the second cartridge drive (MB2k2). The one storage amount sensor (SN1k) senses whether or not the storage amount of the developer in the K (black) color reserve tank (H2k) is a predetermined amount or more. The cartridge control means (C5) controls operation of the K (black) color cartridge drive (MB2k) so that the detection value of the storage amount sensor (SN1k) indicates presence for supplying the developer from the developer cartridge (Kk) being used to the developing unit (Gk).
Therefore, in the image formation apparatus of the invention, the one storage amount sensor (SN1k) detects the developer amount in the reserve tank (H2k) into which developers flow from the two developer cartridges (Kk1 and Kk2), so that it is not necessary to provide the sensor for each developer cartridge. That is, the number of the sensors for detecting the presence or absence of developer can be decreased and therefore the cost can be reduced.